The power transmission apparatus which selectively connects and cuts the driving force (output) of an engine to the wheels of the vehicle, includes a manual transmission (MT) and an automatic transmission (AT), using a torque converter. Although the AT is easy for shifting operation, it has a disadvantage that it is less responsive. On the other hand, the MT has a disadvantage of a large shock during speed changes although it has a good response.
In view of reducing the shock during speed changes and to improve the response, a power transmission apparatus provided with a plurality of clutch sections, has been developed (see Europe Patent Publication No. 1195537 Specification). The power transmission apparatus of the prior art includes an input member rotated by the output of an engine, two clutch sections of a multi-disc type, transmission members extending from outside of the two clutch sections and connected to output shafts, and a selecting mechanism controlled by hydraulics to press and separate a plurality of clutch discs of each clutch section.
In this power transmission apparatus, it is possible to carry out the speed change operation (speed change by a transmission of vehicle), corresponding to its output shaft with the driving force of the input shaft being selectively transmitted via the transmission member corresponding to the clutch section, when any one of the clutch sections is selectively actuated. Such a power transmission apparatus can perform the automatic switching control of the clutch sections in accordance with the velocity of the vehicle and also perform the automatic speed change operation without causing a conspicuous shock in the speed change.
However, in the power transmission apparatus of the prior art, since the transmission members extend from radially outside of the two clutch sections and are connected to the output shafts arranged at the center of the apparatus, the transmission members are arranged so that they cover the clutch sections and the selecting mechanism etc. Thus, the heat radiation from the clutch sections, selecting members, etc. tends to be obstructed. In addition, since one transmission member is formed so that it covers the other transmission member, the size of the clutch discs (driving clutch discs and driven clutch discs) in the clutch sections is differentiated. This makes it difficult to use common parts in the apparatus. Furthermore, since the input means extends from radially outward to radially inward of the power transmission apparatus to form a power transmission path, the structure that includes the selecting mechanism becomes complicated.